Melting points of molecular solids

How do the melting points of molecular solids relate to those of other types of soUds ... 

Ionic solids typically have melting points hundreds of degrees higher than the melting points of molecular solids. Explain. 

SECTION 12.7 Covalent-network solids consist of atoms held together in large networks by cot ent bonds. These solids are much harder and have higher melting points than molecular solids. Important examples include diamond, where the carbons are tetrahedrally coordinated to each other, and graphite where the carbon atoms form hexagonal layers through sp bonds. 

The solidification speed of salol is about 2.3 mm mim at 10°C. Using eqn. (6.15) estimate the energy barrier q that must be crossed by molecules moving from liquid sites to solid sites. The melting point of salol is 43°C and its latent heat of fusion is 3.2 x 10 ° J molecule F Assume that the molecular diameter is about 1 nm. 

P4 Ofi The relatively low melting point of 25 °C indicates a molecular solid. The molecular structure shows that P4 Og is a discrete molecule. Strong covalent bonding holds the atoms in each molecule together, but each molecule is attracted to the others only by dispersion forces. In this molecular solid, little energy is required to overcome dispersion forces and allow P4 Og solid to melt. 

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